Generally, a battery comprises: a battery cell, in which an electrode assembly is mounted; and a cap assembly, which includes a protection circuit board, on which protection circuit chips are mounted, connection terminals, and a cap housing. Specifically, the battery cell includes the electrode assembly, which includes cathodes/separators/anodes, and a case for receiving the electrode assembly such that electrode terminals of the electrode assembly protrude outward from the case and storing a predetermined amount of electrolyte therein. The protection circuit board includes a board part, which is disposed at the upper end of the battery cell and on which a protection circuit electrically connected with the electrode terminals of the battery cell is formed, and external input and output terminals connected to an external device (for example, a wireless terminal, a laptop computer, an electric vehicle, etc.), which is located opposite to the board. The protection circuit board is electrically connected to the battery cell via connection terminals, leads, and a safety element, such as a positive temperature coefficient (PTC) element or a bimetal. These various components are covered by a cap housing while the components are mounted to the battery cell.
Generally, the secondary battery is manufactured by connecting the safety element and the connection terminals (the leads may be further included according to circumstances) to predetermined positions of the battery cell, coupling the protection circuit board to the battery cell, and covering the outside of the battery cell with the cap housing. However, the above-mentioned complicated assembly process is time-consuming even though the assembly process is carried out by skilled workers. Furthermore, the defective ratio during the manufacture of the secondary battery is high due to the multiple steps of the assembly process, and the defective ratio during the use of the secondary battery, especially when external impacts are applied to the secondary battery, is also high due to low coupling force between the components.
In order to solve the above-mentioned problems, there has been proposed a method of manufacturing a secondary battery comprising: placing the battery cell and the cap assembly, which includes the protection circuit board, in a molding device; and injecting resin into the molding device. However, this method has the following problems.
First, the manufacturing process is carried out while the circuit is operated. As a result, when the battery cell and components of the cap assembly are integrally fixed, the battery cell and components of the cap assembly are brought into contact with the molding device, and therefore, the possibility of generating short circuits is very high.
Secondly, when an upper molding unit and a lower molding unit are coupled with each other in the state that the battery cell and components of the cap assembly are temporarily coupled with each other in the molding space of the molding device, the physical pressure is applied to the battery cell depending upon the size of the battery cell, especially, the thickness of the battery cell, and therefore, the possibility of deforming the battery cell is very high.
Thirdly, when melted resin is injected into the molding space of the molding device under high temperature and high pressure, the positions of the battery cell and components of the cap assembly are changed. As a result, the defective product rate is increased.
Fourthly, when the battery cell reaches the high-temperature state in the molding device, the battery characteristics of the battery cell may be changed, and the possibility of explosion of the battery cell is high. Also, when pressure is applied to a battery case, which constitutes the battery cell, in the molding device, the pressure is applied to the welded area of the battery case, where a battery can and a top cap of the battery case are attached to each other by welding, with the result that vents may be formed.
Fifthly, the manufacturing process is carried out while voltage is applied to the battery. For this reason, it is necessary to form a coating layer for preventing occurrence of electrical short circuits at the output terminal side, which is troublesome.
In order to solve the above-mentioned problems, the protection circuit board is integrally formed with the cap housing such that some of the components are formed in the shape of a single body. In this case, however, an assembly step of electrically connecting the safety element, for example, the positive temperature coefficient (PTC) element, the connection terminals, and the leads to the battery cell is further required. As a result, the efficiency of the assembly process is very low even though the number of the assembly steps is reduced.
As described above, the conventional battery manufacturing method has a lot of problems, and therefore, the necessity of a technology to solve the above-mentioned problems is highly increased.